However, the average person will not backup the system,
.. until this person learns by the hard way.
I backup my system and my data regulary and do not expect that a program with another purpose would do that for me.
I don't believe the OP is suggesting that Avast do data backups or system rollback, just that Avast itself should have a rollback function.
Even then, I don't believe it should, rolling back your Antivirus in isolation could have implications, given that AVs are deeply embedded into the OS. For instance compatibility or rather incompatibility with the OS and what about files in the virus chest, etc.
A long time ago backing up was much more difficult than it is now, there are many backup programs around, some are even free. Not to mention, Windows 10 has made it much easier to do a system backup, if you want to rollback, this is a much better way as it isn't rolling back one program in isolation, but everything. However, you have to being regular backups (at least weekly) or you could have a lot of programs that require update.
Until a user loses all of their music, image, emails, data files do they have the lightbulb moment, what if they were backed up.